Electric toothbrush with rigidly connected grip portion and brush portion

ABSTRACT

An electric toothbrush includes a grip portion, a brush portion, and a joint arrangement for connecting the two portions. The joint arrangement has an upper cylinder portion and a lower cylinder portion, with an axis of the upper cylinder portion being inclined a predetermined angle with respect to an axis of the lower cylinder portion. The grip portion is connected to the lower cylinder portion and the brush portion is connected to the upper cylinder portion, so that the grip portion and the brush portion are inclined by the predetermined angle.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims the benefit of priority to Japanese Patent Application Serial No. 2016-051505, filed Mar. 15, 2016, the entirety of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION (1) Field of the Invention

The present invention relates to an electric toothbrush having a grip portion and a brush portion, and more particularly, to the structure of the electric toothbrush.

(2) Description of Related Art

The electric toothbrush in the market has the grip portion and the brush portion with an indicator located in the grip portion. Also, the electric toothbrush in the market has the brush portion angled or inclined with respect to the grip portion. Such an electric toothbrush is disclosed, for example, in US Patent Publication No. 2011-0056033 (corresponding to Japanese Patent Publication No. 2009-268828).

According to US Patent Publication No. 2011-0056033, the indicator is provided on only one side of the electric toothbrush where the bristle is provided, so that the user can view the indicator only when the electric toothbrush is held at a certain angle. It is difficult for the user to see the indicator when the electric toothbrush is held in sideways, particularly when the user is brushing the inside surface of the tooth.

Also, according to US Patent Publication No. 2011-0056033, since the brush portion is angled or inclined with respect to the grip portion, the tension or stress observed at a joint between the grip portion and brush portion will be relatively high, particularly when the user pushes the brush hard against the teeth. There is no detailed description in US Patent Publication No. 2011-0056033 on the structure of connection between the grip portion and the brush portion.

BRIEF SUMMARY OF THE INVENTION (1) Problems to be Solved

The prior art electric toothbrush has such problem that the tension between the grip portion and the brush portion will be relatively high, as explained above. An object of the present invention is to provide an electric toothbrush which has a rigid connection between the grip portion and the brush portion.

(2) Means for Solving the Problems

According to the present invention, an electric toothbrush having a grip portion and a brush portion with an axis of the brush portion being angled or inclined a predetermined angle with respect to an axis of the grip portion, comprises: a stem accommodated in the brush portion, said stem having a cavity for installing a vibration generator, a first screw groove formed at a bottom of the stem, and a first engage member formed adjacent the first screw groove; a cylindrical body included in the grip portion and having a receiving opening; and a stem joint arrangement including a stem joint for connecting the brush portion and the grip portion, wherein said stem joint having an upper cylinder portion and a lower cylinder portion, with an axis of the upper cylinder portion being inclined a predetermined angle with respect to an axis of the lower cylinder portion, and wherein the upper cylinder portion is formed with a second screw groove, and a second engage member adjacent the second screw groove, whereby the lower cylinder portion is inserted in the receiving opening formed in the cylindrical body, and the first screw groove engages with the second screw groove in a screwing manner, and the first engage member engages with the second engage member.

According to an embodiment, the first screw groove is a male screw groove, and the second screw groove is a female screw groove.

According to an embodiment, the first engage member is a projection, and the second engage member is a recess.

According to an embodiment, the stem joint arrangement further includes a stem packing made of rubber and a rubber cover covering the lower cylinder portion.

According to an embodiment, the cylindrical body is formed with a plurality of blocks in the receiving opening, and the lower cylinder portion is formed with a plurality of indents which engage with the blocks.

According to the electric toothbrush of the present invention, since a stem joint having an upper cylinder portion and a lower cylinder portion inclined to each other is used, the grip portion and the brush portion will not be easily separated even when a tension or stress is applied therebetween.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a side view of an electric toothbrush according to an embodiment of the present invention.

FIG. 2 is an exploded view of the electric toothbrush shown in FIG. 1.

FIG. 3 is a perspective view of a circuit board shown in FIG. 2.

FIG. 4 is a perspective partial view of a chassis shown in FIG. 2.

FIG. 5A is a side view of an illumination ring body shown in FIG. 2.

FIG. 5B is a top plan of the illumination ring body shown in FIG. 5A.

FIG. 6 is a cross-sectional view of the illumination ring body taken along line VI-VI shown in FIG. 5B.

FIG. 7 is a cross-sectional partial view of the electric toothbrush shown in FIG. 1.

FIG. 8 is a cross-sectional partial view taken along line VIII-VIII shown in FIG. 7.

FIG. 9 is a cross-sectional partial view taken along line XI-XI shown in FIG. 8.

FIG. 10 is a side view of a stem joint shown in FIG. 2.

FIG. 11 is a cross-sectional view of the stem joint shown in FIG. 10.

FIG. 12 is a perspective view of the stem joint shown in FIG. 11.

FIG. 13 is an exploded view of the stem joint and the stem.

FIG. 14 is a side view of the stem joint and the stem in the connected condition.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, an electric toothbrush 1 according to an embodiment of the present invention is shown. The electric toothbrush 1 has a grip portion 2 and a brush portion 4. An axis X4 of the brush portion 4 is angled or inclined a predetermined angle θ, such as for example but not limited to between about 6 and about 10 degrees, most preferably about 8 degrees, with respect to an axis X2 of the grip portion 2 so that a bristle portion 4 a of the brush portion 4 can be easily held against a user's tooth when the grip portion 2 is held by the user proximate the user's mouth. As will be discussed below, the axis X4 and the axis X2 can be considered to be defined by the upper cylinder portion 42 a and the lower cylinder portion 42 b of the stem joint 42, respectively, in certain embodiments.

Referring to FIG. 2, an exploded view of the electric toothbrush 1 is shown. The grip portion 2 of the electric toothbrush 1 includes an elongated body cover 10, a chassis 20, a battery holder 16, a motor support 62, and an elongated circuit board 50. An intermediate portion including an illumination ring body 30, a stem joint arrangement 40, and a top cover 12, is positioned between and arranged to couple the grip portion 2 to the brush portion 4. The electric toothbrush further includes a stem 80 that is connected to and extends from the intermediate portion. The stem 80 accommodates a DC motor 60 having a cylindrical body, and a vibration shaft 70. A top rubber cover 14 is also provided as part of the intermediate portion. The brush portion 4 includes a replaceable brush 90. A battery to be inserted in the battery holder 16 is a rechargeable battery or a dry cell battery. The replaceable brush 90 is detachably mounted on the stem 80. The replaceable brush 90 covers the stem 80 completely or partially.

In the specification, the term “top” or “upper” refers to the side of the electric toothbrush 1 where the replaceable brush 90 is provided, and the term “bottom” or “lower” refers to the side where the battery holder 16 is provided, such as shown in FIG. 1.

The body cover 10 has an interior cavity, which may be for example, cylindrical, for accommodating the chassis 20, battery holder 16 and circuit board 50. The body cover 10 has a top side and a bottom side opened. The body cover 10 is capable of being gripped or grasped by a user.

As shown in FIG. 3, the circuit board 50 has an elongated board 52 and a light emitting element support plate which is a U-shaped plate 54 firmly connected to a top end of the elongated board 52. The U-shaped plate 54 has two arms 54 a and 54 b extending perpendicularly from the top end of the elongated board 52. Two light emitting elements, such as light-emitting diodes (LEDs) 56 a and 56 b are mounted on one arm 54 a, and another two LEDs 56 c and 56 d are mounted on other arm 54 b, so that four LEDs 56 a, 56 b, 56 c and 56 d are located, when viewed from the top, at four corners of a rectangle, or a square. While four LEDs 56 a, 56 b, 56 c and 56 d are shown and described here, more or fewer LEDs may be located on the plate 54. Moreover, the LEDs may be discrete LED sources or they could include one or more flexible printed or organic LED substrates capable of illumination. Turning ON and OFF of the LEDs 56 a, 56 b, 56 c and 56 d are controlled by a controller mounted on the circuit board 50. The controller includes a micro-processor and an acceleration sensor. The acceleration sensor is used for detecting the angle of the toothbrush held by a user. As shown in FIG. 2, a connector 58 extends through the center of the U-shaped plate 54 for electrical connection with the DC motor 60.

Referring to FIG. 4, a top portion of chassis 20 is shown. Chassis 20 has a pair of fingers 22 a and 22 b for holding the elongated board 52, a pair of shoulders 24 a and 24 b, and a neck portion 26. The neck portion 26 has a center hole in the direction of axis X2, with recesses 26 a and 26 b formed at opposite sides thereof. Through-holes 28 and 29 are formed, respectively, under the shoulders 24 a and 24 b. The through-holes 28 and 29 have bottom surfaces 28 a and 29 a, respectively, which are flattened for receiving thereon, respectively, the two arms 54 a and 54 b of the U-shaped plate 54.

The two arms 54 a and 54 b of the U-shaped plate 54 are inserted in the through-holes 28 and 29, respectively, as shown in FIG. 2, and the elongated board 52 is firmly held between the fingers 22 a and 22 b. Also, the connector 58 extends through the center hole in the neck portion 26. When the arms 54 a and 54 b of the U-shaped plate 54 are placed on bottom surfaces 28 a and 29 a of the through-holes 28 and 29, the LEDs 56 a, 56 b, 56 c and 56 d on the two arms 54 a and 54 b face the top, i.e., in the direction of axis X2.

The through-holes 28 and 29 further have top slanted surfaces 28 b and 29 b which are for reflecting purposes and are angled about 45 degrees with respect to the direction of axis X2 so that light rays emitted from the LEDs, particularly, from 56 a and 56 c reflect on the slanted surfaces 28 b and 29 b, and direct outwardly in a radial or otherwise substantially perpendicular direction with respect to the axis X2. In FIG. 4, only two slanted surfaces 28 b and 29 b are shown, but there are two more slanted surfaces 28 c and 29 c on the other side in FIG. 4. The slanted surfaces 28 b, 28 c, 29 b and 29 c are angled about 45 degrees with respect to axis X2 in radial direction, so that slanted surfaces 28 b, 28 c, 29 b and 29 c are arranged in a manner similar to an umbrella surface. Each of the slanted surfaces 28 b, 28 c, 29 b and 29 c is flat, but it may be curved. The light rays emitted from the LEDs 56 a, 56 b, 56 c and 56 d in the direction of axis X2 are reflected on the slanted surfaces 28 b, 28 c, 29 b and 29 c, and are further directed in the radial direction or otherwise substantially perpendicular with respect to the axis X2.

Referring to FIGS. 5A and 6, the illumination ring body 30 is shown which is made of a substantially transparent or translucent material, such as synthetic resin. The illumination ring body 30 has hollow cylindrical body 30 a with an illumination ring 30 b circumferentially surrounding the cylindrical body 30 a. The illumination ring 30 b is an annular structure that protrudes from the outer surface of the illumination ring body 30, thereby forming an annular flange. The illumination ring 30 b is inclined or angled a predetermined angle θ, such as for example but not limited to between about 6 degrees and about 10 degrees, most preferably about 8 degrees, with respect to a plane perpendicular to the axis X2. The cylindrical body 30 a, which is a part of the grip portion 2, has opposite ends opened, and has an internal plate 30 c inside the cylindrical body 30 a so as to provide a skirt wall 30 d below the internal plate 30 c. The center of the internal plate 30 c is formed with an opening 30 e (FIG. 5B) in a shape of semi-circle to fittingly match the semi-circle cross-section of the neck portion 26 with recesses 26 a and 26 b, as best shown in FIG. 8. Above the internal plate 30 c, the cylindrical body 30 a has a receiving opening 30 i for fittingly receiving a lower cylinder portion 42 b of the stem joint 42 covered with a bottom rubber cover 46, as will be described later. While the illumination ring body 30, including the cylindrical body 30 a and illumination ring 30 b, is shown and described as being cylindrical, one of skill in the art will recognize that other shapes and geometries are possible depending on the shape and design of the grip portion 2 of the electric toothbrush 1.

As shown in FIG. 5B, on the top surface of the internal plate 30 c, there are three blocks 30 f, 30 g and 30 h formed at corners between the internal plate 30 c and the cylindrical body 30 a.

On the outside of the illumination ring body 30, a pair of projections 30 p are provided, as shown in FIG. 5A.

The chassis 20 provided with the circuit board 50 is inserted into the body cover 10 from the bottom opening, and held inside the body cover 10 at a position shown in FIG. 4, so that the top end of the chassis 20 stays a little below the top opening of the body cover 10.

As shown in FIGS. 7 and 8, the illumination ring body 30 is mounted on the shoulders 24 a and 24 b of the chassis 20 such that neck portion 26 of the chassis 20 is fittingly inserted into the opening 30 e. At this position, the bottom surface of the internal plate 30 c rests on the shoulders 24 a and 24 b of the chassis 20, and the skirt wall 30 d circumferentially surrounds, at least in part, the slanted surfaces 28 b, 28 c, 29 b and 29 c. The outer surface of the illumination ring body 30 below the illumination ring 30 b is fittingly inserted into the top opening of the body cover 10 such that the projections 30 p on the illumination ring body 30 engage with complementary recesses (not shown) formed on the inside surface of the body cover 10 to couple the body cover 10 to the illumination ring body 30.

As shown in FIG. 9, the light emitted from the LEDs, such as 56 a and 56 b, reflects on the slanted surfaces 28 b and 28 c, and direct toward the skirt wall 30 d, so that the light is optically transmitted within inside and throughout the illumination ring body 30. Some of this light will be transmitted into the illumination ring 30 b and exit an outer annular surface of the illumination ring 30 b that forms a portion of the exposed outer surface of the electric toothbrush.

As shown in FIG. 7, a majority of the illumination ring body 30 is concealed such that the portion below the illumination ring 30 b is concealed by body cover 10, and the portion above the illumination ring 30 b is concealed by top cover 12. Body cover 10 and top cover 12 may both be substantially opaque and may be made from the same or different materials. In this embodiment, only the illumination ring 30 b can be viewed directly from the outside of the electric toothbrush 1.

The outside surface of the illumination ring body 30, with the exception for the illumination ring 30 b, can be coated with a reflector paint so that light that has entered the illumination ring body 30 from the inside surface of the skirt wall 30 d can be maintained within the illumination ring body 30 until said light can exit the illumination ring 30 b. Stated simply, the reflector paint will prevent and/or minimize leakage of light. Thus, light from the illumination ring 30 b can be outputted with high intensity outside the electric toothbrush 1.

Since the illumination ring 30 b is provided in a viewable manner completely, i.e., 360 degrees, around the electric toothbrush 1 just above the grip portion 2, it is possible for the user to view the lighting of the illumination ring 30 b no matter which angle the electric toothbrush 1 is held. It should be noted, however, that while the illumination ring 30 b is an annular continuous structure in the illustrated embodiment, in other embodiments the illumination ring 30 b may be in the form of spaced-apart segments that collectively define a segmented ring structure.

The lighting of the illumination ring 30 b can be effected in various occasions in various modes, as explained below.

The first occasion is when a bristle portion of the electric toothbrush 1 is held at about 45 degrees above or below the plane level so that the bristle touches the tooth pockets of the upper or lower tooth from the outside or inside the tooth.

The second occasion is when the electric toothbrush 1 is held at about 90 degrees above or below the plane level so that the bristle touches the occlusal surface of the molar or pre-molar tooth.

The third occasion is when the electric toothbrush 1 is held at about the plane level so that the bristle touches the front face or back face of the tooth perpendicularly.

Each of the above occasions can be detected by the acceleration sensor in a manner disclosed, for example, in U.S. Publication No. 2012/0251975 (corresponding to Japanese Publication No. JP2011-156204) or Japanese Publication JP2009-291316, which are herein incorporated by reference in its entirety.

The lighting mode can be changed with respect to different occasions. For example, a first lighting mode can be an ON and OFF mode such that the LEDs are turned ON when the above explained target angle is detected.

A second lighting mode can be a graduation variable mode such that the LEDs change the strength of the light (i.e., the intensity of the light) to glow brighter as the toothbrush angle reaches the target angle.

A third lighting mode can be a blinking mode such that the frequency of ON and OFF of the LEDs becomes higher as the toothbrush angle reaches the target angle.

In one embodiment, the lighting can be effected only in one of the three occasions explained above using any one of the three lighting modes.

Referring to FIG. 2, the stem joint arrangement 40 includes a stem joint 42, a stem packing 44 and a bottom rubber cover 46.

Referring to FIGS. 10 and 11, the stem joint 42 has an upper cylinder portion 42 a and a lower cylinder portion 42 b. The upper cylinder portion 42 a has its axis aligned with axis X4, and the lower cylinder portion 42 b has its axis aligned with axis X2.

The upper cylinder portion 42 a has an inside surface formed with female screw groove 42 c. The top surface of the upper cylinder portion 42 a is formed with a slanted projection 42 d and a stopper projection 42 e. The slanted projection 42 d has one side formed with a slanted wall and the other side formed with an upright wall. The stopper projection 42 e has opposite sides formed with upright walls. A receiving recess 42 f, which is a second engage member (a first engage member will be described later), is formed adjacent the screw groove 42 c, such as between the projections 42 d and 42 e, particularly between the upright wall of the slanted projection 42 a and the upright wall of the stopper projection 42 e.

Referring to FIG. 12, the lower cylinder portion 42 b has a recessed ring portion 42 g and three legs 42 h, 42 i and 42 j. As shown, legs 42 i and 42 j are mirror images of one another and together are positioned diametrically opposite the leg 42 h. An indent 42 k is formed between legs 42 h and 42 i. An indent 42 l is formed between legs 42 h and 42 j. An indent 42 m is formed between legs 42 i and 42 j.

The stem packing 44 as shown in FIGS. 2 and 7, made of rubber or a like material, is fittingly inserted in the recessed ring portion 42 g (see FIGS. 10-12). The bottom rubber cover 46 as shown in FIGS. 2 and 7 is fittingly mounted on the lower cylinder portion 42 b covering each of the legs 42 h, 42 i and 42 j separately (see FIGS. 10-12). Accordingly, indents 42 k, 42 l and 42 m appear on the outside of the bottom rubber cover 46.

Next, the connection between the lower cylinder portion 42 b and the illumination ring body 30 is explained.

With reference to FIGS. 2 and 7, the lower cylinder portion 42 b mounted with the bottom rubber cover 46 is fittingly inserted in the receiving opening 30 i of the hollow cylindrical body 30 a of the illumination ring body 30 such that indents 42 k, 42 l and 42 m existing on the outside of the bottom rubber cover 46 fittingly receive three blocks 30 g, 30 h and 30 f, respectively. Accordingly, the lower cylinder portion 42 b is prevented from being freely rotated in the hollow cylindrical body 30 a.

As shown in FIG. 7, stem 80 has an elongated cavity 86 for receiving a vibration generator including the vibration shaft 70 and the DC motor 60. The vibration shaft 70 includes an extension shaft 72 made, for example, of synthetic resin, such as POM (polyoxymethylene), and an eccentric shaft 73 which may be, for example, made of metal. The extension shaft 72 of the vibration shaft 70 includes a collar portion 74 provided close to a bottom end, a resilient shaft portion 75 and a connecting portion 76 which are integrally formed by synthetic resin. The bottom end face of the extension shaft 72 is formed with a recess to be engaged with a shaft of the DC motor 60. DC motor 60 has two wires extending from a bottom face thereof for electric connection with the circuit board 50 through connector 58. The vibration shaft 70 and the DC motor 60 are placed in the elongated cavity 86 and held in the cavity by the motor support 62.

The eccentric shaft 73 of the vibration shaft 70 includes an eccentric portion 77 and an axial shaft portion 78. The bottom end of the eccentric portion 77 is firmly connected to the connecting portion 76 by molding and the upper end of the eccentric portion 77 is provided with the axial shaft portion 78.

When the vibration shaft 70 rotates about its axis by the DC motor 60, the eccentric portion 77 generates a high frequency vibration which is transmitted to the stem 80 and to the brush 90. The resilient shaft portion 75 has a flexibility to receive the high frequency vibration of the eccentric portion 77.

Stem 80 is also formed by synthetic resin, such as for example, POM. A recessed hole 87 is formed at the end of the elongated cavity 86. The recessed hole 87 slidably receives the axial shaft portion 78. The elongated cavity 86 accommodates therein the vibration shaft 70 and the DC motor 60. The vibration shaft 70 is freely rotated in the elongated cavity 86. The recessed hole 87 serves as a bearing for freely holding the axial shaft portion 78. The vibration shaft 70 freely rotates inside the elongated cavity 86 even under high frequency vibration.

Since the recessed hole 87 serves as the bearing, it is not necessary to provide a separate bearing arrangement for rotatably holding the axial shaft portion 78.

Referring to FIG. 13, a lower end portion of the stem 80 is shown in detail. Stem 80 includes a collar 82, and a male screw groove 84 below the collar 82. A projection 85, which is a first engage member, is formed adjacent the screw groove 84, such as immediately under the collar 82, i.e., near the end of the screw groove 84.

Stem 80 is firmly connected to the stem joint 42 such that the male screw groove 84 of stem 80 is driven into the female screw groove 42 c of the stem joint 42, as the stem 80 rotates about its axis X4. When the stem 80 rotates a predetermined number of turns, the projection 85, which is the first engage member, slides over the slanted wall of the slanted projection 42 d, and falls into the receiving recess 42 f, which is the second engage member, as best shown in FIG. 14. At this point, stem 80 is prevented from a further rotation in either direction and is retained at a desired and predetermined rotated position from the viewpoint of balance as well as to ensure that the brush 90 is properly oriented relative to the grip portion 2 when attached. The projection 85, which is the first engage member, and the receiving recess 42 f, which is the second engage member, can be formed in opposite relationship, or any other engaging or retaining arrangement can be used. The male and female screw grooves 84 and 42 c can be provided in opposite relationship.

As shown in FIGS. 2 and 7, the top rubber cover 14 is mounted on the stem 80 such that the bottom face of the top rubber cover 14 abuts against the upper surface of the collar 82. Then, the top cover 12 is mounted on the stem 80 such that the bottom face of the top cover 12 abuts against the upper surface of the illumination ring 30 b.

According to an embodiment, suitable bonding agent is used in at least in one or more of the following instances: (a) between elongated body cover 10 and illumination ring body 30, (b) between illumination ring body 30 and stem joint 42, and (c) between stem joint 42 and stem 80.

According to the above described embodiment, the slanted surfaces 28 b, 28 c, 29 b and 29 c are provided in the chassis 20, but can be provided at any other places, such as at the bottom surface of the internal plate 30 c of the illumination ring body 30. In still another embodiment, the slanted surfaces may be omitted and the light emitting elements 56 a-d will be arranged to emit light directly into the illumination ring body 30. Additionally, while the illumination ring 30 b is illustrated as being between the grip portion 2 and the brush portion 4, and more specifically the grip portion 2 and the intermediate portion, in other embodiment, the illumination ring 30 b may be located at a lower position and entirely within the grip portion 4 or entirely within the intermediate portion.

INDUSTRIAL APPLICABILITY

The electric toothbrush can be used for oral health care.

KEYS TO THE REFERENCE NUMBERS

1 . . . electric toothbrush, 2 . . . grip portion, 4 . . . brush portion, 10 . . . body cover, 12 . . . top cover, 14 . . . top rubber cover, 16 . . . battery holder, 20 . . . chassis, 22 a, 22 b . . . fingers, 24 a, 24 b . . . shoulders, 26 . . . neck portion, 26 a, 26 b . . . recesses, 28, 29 . . . through-holes, 28 b, 28 c, 29 b, 29 c . . . slanted surfaces, 30 . . . illumination ring body, 30 a . . . cylindrical body, 30 b . . . illumination ring, 30 c . . . internal plate, 30 d . . . skirt wall, 30 e . . . opening, 30 f, 30 g, 30 h . . . blocks, 40 . . . stem joint arrangement, 42 . . . stem joint, 42 c . . . female screw groove, 42 d . . . slanted projection, 42 e . . . stopper projection, 42 h, 42 i, 42 j . . . legs, 42 k, 42 l, 42 m . . . indents, 44 . . . stem packing, 46 . . . bottom rubber cover, 50 . . . elongated circuit board, 52 . . . elongated board, 54 . . . U-shaped plate, 56 a, 56 b, 56 c, 56 d . . . LEDs, 60 . . . DC motor, 62 . . . motor support, 70 . . . vibration shaft, 80 . . . stem, 90 . . . replaceable brush 

The invention claimed is:
 1. An electric toothbrush having a grip portion and a brush portion with an axis of the brush portion being angled or inclined at a predetermined angle with respect to an axis of the grip portion, said electric toothbrush comprising: a stem accommodated in the brush portion, said stem having a cavity for installing a vibration generator, a first screw groove formed at a bottom of the stem, and a first engage member formed adjacent the first screw groove; a cylindrical body included in the grip portion and having a receiving opening; and a stem joint arrangement including a stem joint for connecting the brush portion and the grip portion, wherein said stem joint having an upper cylinder portion and a lower cylinder portion, with an axis of the upper cylinder portion being inclined a predetermined angle with respect to an axis of the lower cylinder portion, and wherein the upper cylinder portion is formed with a second screw groove, and a second engage member adjacent the second screw groove, whereby the lower cylinder portion is inserted in the receiving opening formed in the cylindrical body, and the first screw groove engages with the second screw groove in a screwing manner, and the first engage member engages with the second engage member.
 2. The electric toothbrush as claimed in claim 1, wherein the first screw groove is a male screw groove, and the second screw groove is a female screw groove.
 3. The electric toothbrush as claimed in claim 1, wherein the first engage member is a projection, and the second engage member is a recess.
 4. The electric toothbrush as claimed in claim 1, wherein the stem joint arrangement further includes a stem packing made of rubber and a rubber cover covering the lower cylinder portion.
 5. The electric toothbrush as claimed in claim 1, wherein the cylindrical body is formed with a plurality of blocks in the receiving opening, and the lower cylinder portion is formed with a plurality of indents which engage with the blocks.
 6. An electric toothbrush having a grip portion and a brush portion, said electric toothbrush comprising: a stem in the brush portion; a cylindrical body included in the grip portion and having a receiving opening; and a stem joint arrangement including a stem joint, said stem joint having an upper cylinder portion and a lower cylinder portion, with an axis of the upper cylinder portion being inclined a predetermined angle with respect to an axis of the lower cylinder portion; and wherein the upper cylinder portion engages a bottom of the stem, and the lower cylinder portion is received in the receiving opening of the cylindrical body, thereby connecting the stem to the grip portion such that the brush portion extends along the axis and the grip portion extends along the axis. 